This invention relates to data transmission networks, and more particularly, to a fiber optic local area network partitioned by bulkheads.
Linear bus and reflective star architectures have been employed in autonomous fiber optic networks. (In an autonomous data bus the bus architecture is such that all terminals of the bus can hear the transmission of any other terminal, regardless of whether or not data transfer is necessary between all terminals. Thus, each terminal can independently determine the bus idle state.) The linear bus utilizes two bus fibers, one for each direction of information flow. A linear bus also can be built with a single bidirectional bus fiber at the expense of an additional power loss. The star architecture is implemented with a reflective star coupler at the heart of the network.
With the two-fiber linear bus a separate light emitter diode (LED) is used to transmit in each direction on the bus through 2.times.2 directional optical couplers. A top (or uppermost) terminal receives optical data transmitted from a center terminal through an upward flow (ie., from the terminal to the controller) bus fiber. A lower terminal receives optical data transmitted from the center terminal through a downward flow (ie., from the controller to the terminals) bus fiber. In this way all terminals on the bus hear the transmission of all other terminals.
The reflective star bus architecture, has optical power signals launched onto the bus through 1.times.2 directional couplers. A signal input at any port of the star coupler is reflected to all ports as output from the coupler. Signals are then routed to each terminal on the bus. The 1.times.2 couplers at the terminals provide the capability to launch onto and tap off of the optical bus.
The linear bus requires twice as many LED sources and about fifty percent more connectors to implement and also has a somewhat higher power budget requirement than the architecture of the present invention.
The reflective star architecture requires much more fiber than the preferred embodiment of the present invention, and oftentimes requires many more connectors than the architecture of the present invention when terminals are separated by bulkhead surfaces. Therefore, a bus architecture is desired which provides the capabilities for autonomous bus operation while maintaining power budget and component efficiency.
The preferred embodiment of the present invention utilizes a transmissive star coupler at each of the remotely located terminal groups to funnel signals onto a single fiber for a data transfer, over some relatively large distance, to a centralized reflective star coupler. Increased fiber efficiency, as well as a reduction in the number of bulkhead connectors that is required in some applications, is realized in the present invention because only a single fiber is required to carry optical power signals to each remotely located group of terminals. Also, a space and weight savings is realized with the architecture of the present invention because of the reduced fiber and connector demands.
The present invention applies to the field of fiber optic local area networks and is particularly applicable in networks which are partitioned by bulkheads (bulkheads can be walls, partitions, . . . to separate compartments). The invention finds particular application as a data bus architecture for a commercial aircraft primary flight controls system, where the relative location of terminals are generally partitioned by bulkheads.
The fiber optic network of the present invention can be utilized to link terminals in a network, independent of whether or not the network is autonomous or utilizes a centralized bus control protocol. The architecture of the present invention is particularly useful in networks where two or more similar size groups of terminals are separated by bulkheads or a large distance. The present invention provides an advantage in fiber and connector requirements over star network and also yields weight and space savings. The invention finds particular application in "fly-by-light" aircraft.